Code division multiple access (CDMA) technology has improved tremendously since its inception. Today, CDMA systems use radio link protocol (RLP) packets to send data at high speeds. Currently fixed packet-size is used for transferring data. Current practices involve placing a single packet of fixed size in a frame and sending the frame to fit a channel condition. The frames used include a cyclic redundancy check (CRC) for detecting error in the frame.
Channel conditions differ greatly in a system. A channel may be operating under good, bad, or other various intermediate conditions. A channel may also be prone to more error when there is interference or propagation loss. For example interference from other users will add noise that is distributed normally and effects the condition of the channel. Multi-path conditions that occur between a system and a mobile unit adding bursts of noise when the mobile is in motion may also cause interference. Various external or internal features of a system may also vary the channel conditions.
There are many disadvantages to using a fixed packet-size for sending data. One disadvantage to using a fixed packet-size is that the packet-size may not fit a particular channel condition and get rejected. For example in a good channel condition a longer packet-size is preferred due to low CRC overhead and in a bad channel condition a shorter packet-size is preferred due to low transmission overhead. Sending a fixed packet-size for all the conditions creates difficulty due to power and system overloads, furthermore, the fixed size may frequently not fit the particular channel condition thereby resulting in the packet being rejected.
Another disadvantage of using a fixed packet-size in a frame equipped with a CRC error detection system is that any frame that does not pass the CRC is completely discarded. A frame does not pass CRC if the packet-size within the frame does not match the allowable size for the current channel condition. For example a large frame with a large packet-size may have a couple of bit errors because it does not fit the current channel condition, thus, the frame will be discarded completely, wasting all the information in the frame.
In addition when a channel is prone to more error the chance of receiving a fixed size packet correctly decreases, further if a packet is sent during this period which doesn't comply with allowable packet-size for the current channel condition it will be rejected.